Content Adaptation for Context-Aware Service
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176 JOURNAL OF SOFTWARE, VOL. 7, NO. 1, JANUARY 2012 Content Adaptation For Context-Aware Service Jui-Fa Chen Department of Computer Science and Information Engineering, Tamkang University, New Taipei City, Taiwan Email: [email protected] Ying-Hong Wang, Jingo Chenghorng Liao, Chen-An Wang Department of Computer Science and Information Engineering, Tamkang University, New Taipei City, Taiwan Email: [email protected], [email protected], [email protected] Abstract—The current and developing trend for consumers used. In the fact, the other problem is all computational is to access web contents and applications anytime, overheads are shifted to the client in the system. anywhere, and on any devices. Most of Internet services and In server-based adaptation, the functionalities of the most of web contents have been designed for desktop web server are enhanced on content adaptation. computers, and often contain rich medias, such as images, Transmission time is reduced because the contents have audios, and videos. However, some devices are different from network connectivity, processing power, storage already been adapted. Traditionally, some variants of the capacity, display size, and formative handling capability. In same content are stored on the server, and it selects to many cases, the content designed for computers is not match the client identification. A common way for suitable for new (and often mobile) devices. Therefore, providing content to different devices is to store the content adaptation is needed in order to optimize the service content in Extensible Markup Language (XML) and uses for different devices and access methods. This research Extensible Style Language Transformation (XSLT) to discusses the context issues for web content adaptation. The convert the content to the appropriate makeup language. CC/PP and UAProf are two related standards that define In the proxy-based adaptation approach, a proxy server the format to describe the capabilities of devices for analyzes and transcodes the contents before sending the accessing content. A context-aware environment should allow adaptive access to context information. In this paper, results to the client. Content servers and proxies need to first we proposed an inference mechanism for context-aware know what kind of device from the request in order to service. Through this inference mechanism, users using send the right contents different devices can get appropriate contents based on Context is the information that characterizes the inference results. Second, we can demonstrate the interactions between humans, applications and the correlation between classes and individuals, and provide surrounding environments [3]. Many researchers have better scalability by means of building ontologies. Lastly, tried to define context, such as Schilit et al. who assigned SWRL depends on ontology based rule languages. Rules context to three categories [4]: computing context, user written based on SWRL can directly use an established context, and physical context. Muldoon et al. defined object relationship from ontology. context as an aggregation of the user’s location, previous Index Terms—Context-Aware, Adaptation, SWRL, activities, and preferences [5]. J. Sun adopted the same Inference, UAprof, Web Services definition and even added physiological information to user context [6]. Huang et al. defined the context of an entity as a collection of semantic situation information I. INTRODUCTION that characterized the entity’s internal features or operation and external relations under a specific situation. Adaptation means a process of selection, generation, or Context-aware computing, as discussed by Dey and modification of contents (texts, images, audios and videos) Abowd, refered to the ability of computing devices to to suit the user’s computing environment and usage detect and sense, and interpreted and responded to aspects context. In general, web pages incorporate a variety of of a user’s local environment and the computing devices media types and when using a PC connected to a website, themselves [7]. Context-aware content adaptation it is possible to see the original web page (without dynamically adapts behavior to the user’s current adaptation) with headings, photos, texts and videos. situation without user intervention. When accessing the same service with a mobile device, In this paper, we address a content adaptation approach the image is compressed. The text is summarized to one for a proposed context-aware architecture. The next paragraph and the video is delivered as text or an image, section offers a survey of related researches about this depending on bandwidth and the capabilities of the approach. Section 3 describes the context-aware system device. architecture. Content adaptation is presented in section 4. Adaptation can take place on a client, a server or an And the final section is conclusions and future research intermediate proxy [1][2]. In a client-based adaptation that we presented. approach, the client needs to receive the same media encoding in different versions although only one will be II. RELATED WORK © 2012 ACADEMY PUBLISHER doi:10.4304/jsw.7.1.176-185 JOURNAL OF SOFTWARE, VOL. 7, NO. 1, JANUARY 2012 177 With the development of network technology, the web constrain conforming XML documents to a specific content can offer more and more abundant. However, vocabulary and a specific hierarchical structure. There are there are certain limitations among mobile devices and two types of documents, a schema document and multiple we are unable to fill all information in these devices. instance document, that conform to the schema. A Context-aware technology can perceive the status of schema can play two roles [20]: mobile devices and can adapt the contents for better z Template for a form generator to generate presentation, especially for the limitations on network instances of a document type. connectivity, processing power, storage capacity, display z Validator to ensure the accuracy of documents. size, and formative handling capability. RDF: The Resource Description Framework (RDF) is an XML-based language to describe resources. While the A. The Semantic Web definition of “resource” can be quite broad, let’s begin Most meaning on the web today is inferred by users with the common understanding of a resource as an who read web pages. The semantic web is supposed to electronic file available via the web. Such a resource is make data on the web readable and understandable, both accessed via a Uniform Resource Locator (URL). In RDF to users and to machine. [18]. Figure 1 illustrated model, a statement is often called a “triple” because it has semantic web stack. three parts. Those three parts are described in terms of the grammatical parts of a sentence: subject, predicate, and object. In common, the predicate is called the property of the triple. And the object is called the value of the triple. Figure 2 displays the elements of the tri-part model. Figure 2. The RDF Triple To play its role of describing data and meta data, RDF needs to include the following capabilities [21]: z Able to describe most kinds of data that will be available. z Able to describe the structural design of data sets. Figure 1. Semantic Web Stack z Able to describe relationships between bits of data. XML: XML is not a language. It is actually a set of RDF defines three special resource types to group syntax rules for creating semantically rich markup resources or literal [19] [21] [20]: languages in a particular domain. The first key principle z Bag: The element is used to describe a list of of XML is markup and is separated from content. An values that does not has to be in a special order. XML element is an XML container, consisting of a start Duplicates are allowed in the collection. tag, content (other elements, text, or both), and an end tag z Sequence: The element is used to describe an (except for empty elements), which use a single tag ordered list of values. Duplicates are allowed in denoting both the start and end of the element. Elements the collection. A reason to use a sequence would maybe have zero or more attributes, each with its be to preserve the alphabetical order of elements. associated value. The second key principle of XML is z Alternate: The element is used to describe a that a document is classified as a member of a type by choice of multiple values or resources. This is dividing its parts, or elements, into a hierarchical referred to as a choice in XML. Some examples structure known as a tree [19][20]. would be a choice if image format (JPG, GIF, A well-formed XML document must satisfy the PNG, GMP). following requirement [20]: There are multiple reasons that RDF has been weak z It must be a tree with a single root. [21]: z Every start tag must have a matching end tag. z RDF does not yet play well with XML z All attributes must be quoted. documents. z Empty tags must have a trailing slash. z Parts of RDF are complex. z All entities must be declared. z Early RDF examples are weak. z Child elements must be properly nested. There are five primary reasons that RDF’s adoption The validity of an XML document can be determined will grow [21]: by comparing it to a specified Document Type Definition z Improved tutorials (DTD) or a specified XML Schema document. XML z Improved tool support schema is a definition language. That enables you to z Improved XML schema integration © 2012 ACADEMY PUBLISHER 178 JOURNAL OF SOFTWARE, VOL. 7, NO. 1, JANUARY 2012 z Ontologies z Generic or common sense ontology: aim at z Non-contextual modeling capturing general knowledge about the world. RDF schema is used to define vocabularies. It used z Representational ontology: do not commit RDF to define a standard set of predicates that enable themselves to any particular domain.